The invention relates to a motor vehicle having at least two drive assemblies in the form of an internal-combustion engine and an electric motor as well as having a fuel cell for providing electric energy. Such a motor vehicle is known, for example, from German Patent document DE 102 27 530 A1.
Based on the above, it is an object of the invention to provide a motor vehicle which, while its practicality is high, makes it possible to be operated purely electrically to a limited extent, particularly without any significant limitation of the usage possibilities of the interior and of the luggage compartment in comparison to a conventional motor vehicle.
This and other objects are achieved by providing a motor vehicle having at least two drive assemblies in the form of an internal-combustion engine and an electric motor, as well as having a fuel cell for providing electric energy, wherein the internal-combustion engine and the fuel cell are arranged in an engine compartment at a front end section of the motor vehicle.
It is a central aspect of the invention to provide a comparatively small-dimensioned fuel cell in addition to an internal-combustion engine in an engine compartment existing at the front end section of the motor vehicle. This deliberate dimensioning of the fuel cell in an order of magnitude, that is preferably sized for the operation of the motor vehicle in inner-city areas, results in the possibility of arranging the internal-combustion engine as well as the fuel cell in a single compartment of the motor vehicle, specifically the engine compartment.
In this case, the current generated by the fuel cell is fed directly, or by way of a temporary storage in a storage unit for electric energy, to the electric motor. If the fuel cell is operated by use of hydrogen, which is carried along in the motor vehicle, the possibility arises of being able to move the motor vehicle in the electric operation without the emission of pollutants. For this purpose, the fuel cell is designed as a low-temperature fuel cell that is fed by means of hydrogen from a tank specifically provided for this case.
In order to be able to accommodate the fuel cell beside the internal-combustion engine in the engine compartment of the motor vehicle, the internal-combustion engine has to have a correspondingly small size and/or be arranged in a correspondingly space-saving manner. In a preferred embodiment of the invention, an internal-combustion engine is installed transversely with respect to the driving direction and drives the wheels of the front axle by way of a transmission and drive shafts.
In a preferred embodiment of the invention, the internal-combustion engine and the fuel cell are thermally decoupled from one another. In the construction as a low-temperature fuel cell with the direct feeding of hydrogen, the fuel cell can thereby be operated in the optimal temperature range to approximately 60° C.
In an advantageous further development of the invention, an arrangement of the internal-combustion engine is suitable here in such a manner that the outlet side of the internal-combustion engine faces away from the fuel cell. The internal-combustion engine is preferably arranged in the front area of the engine compartment, with a positioning of the exhaust gas manifold facing the driving direction, while the fuel cell is situated in the rear section of the engine compartment, directly in front of the so-called front wall which separates the engine compartment from the passenger compartment of the motor vehicle. The thermal shielding of the fuel cell with respect to the internal-combustion engine is facilitated by this configuration.
Fuel cell power in the order of magnitude of approximately 5 kW is sufficient for the speeds at which motor vehicles move in city areas. The range during a purely electric operation is determined by the amount of the carried-along hydrogen. For higher speeds and ranges in areas outside the city, the internal-combustion engine is provided, which is supplied from a separate tank for fuel (gasoline, diesel, natural gas). The internal-combustion engine can naturally also be operated by use of hydrogen (from a single tank).
For acceleration operations in areas within cities, which cannot be managed with sufficient dynamics by means of the current supplied directly from the deliberately small-dimensioned fuel cell, an accumulator for electric energy is provided, so that the acceleration operations can be accomplished by the use of additional electric energy from the accumulator. While a fairly small drive power is sufficient for constant travel in an area within a city, a motor vehicle designed for the transport of from four to five persons, along with a load, requires a clearly higher drive power in the acceleration phases, for example, when starting to move from a traffic light. These dynamic operating phases of the motor vehicle in the area within a city can be managed by the electric accumulator, which is configured as a temporary storage device. On the one hand, the temporary storage device is charged during constant travel by the fuel cell itself by the feeding of excessive electric energy. In addition, electric energy obtained by recuperation in the coasting operation and during the deceleration of the motor vehicle can be fed into the temporary storage device. The recuperation results in a clear improvement of the energy balance for the operation of the motor vehicle.
In a particularly advantageous manner, the storage unit is arranged in the area of the transmission tunnel, thus in the area between the two front seats. The transmission tunnel preferably extends beyond the area of the front seats toward the rear and continues in the floor area in front of the rear seats and below the rear seats. Such a transmission tunnel is generally known, for example, in the case of motor vehicles having a front engine and a rear axle drive and is used for accommodating a drive shaft (cardan shaft). In the case of motor vehicles having a drive concept without a cardan shaft, the installation space in the area of the transmission tunnel is available for other purposes, as in this case for accommodating the electric storage unit. The electric storage unit can therefore be housed in a particularly protected area of the motor vehicle, considerably protected from damage in the case of a collision of the motor vehicle because, in the event of a frontal, rear and lateral impact, the storage unit is in each case arranged far away from the impact site.
Since the electric storage unit for the operation of the motor vehicle within a city area has to accommodate only comparatively small amounts of energy, in a further aspect of the invention, the storage unit has a plurality of double layer capacitors. These capacitors, also called “supercaps” or “ultracaps”, are distinguished by high robustness with respect to mechanical stress. They have a long service life and do not have to be cooled. This results in advantages, for example, in comparison to lithium ion batteries, which, although they have a higher capacitance, are clearly more sensitive and, as a rule, have to be connected to a cooling circuit. Naturally, however, lithium ion batteries can also be used, as can any other known types of accumulators for electric energy.
In a further development of the invention, at least one fuel tank is provided for a fuel cell and/or for the internal-combustion engine in the area in front of the rear axle. Just like the area of the transmission tunnel, this area is also distinguished by the fact that it is very protected from damage because, even at fairly high collision speeds, comparatively slight deformations of the vehicle structure will occur in this area. In particular, a tank for hydrogen can be accommodated in this area in a particularly secure fashion.
In a further development of the invention, the electric motor directly drives the wheels of the rear axle preferably by way of a transmission. For this purpose, the electric motor is arranged in a space-saving manner directly adjacent to the rear axle.
Additional components for operating the electric motor, such as an electronic power unit, a DC-DC converter, an inverter or other control and automatic control devices can be arranged in a particularly advantageous manner adjacent to the electric motor in that the space in the lower area of a rear luggage compartment of the motor vehicle is utilized. Although this slightly reduces the usable luggage compartment volume of the vehicle, a relatively large volume will still remain for the accommodation of the luggage, so that, in comparison to a conventional motor vehicle, the practical utility of the motor vehicle is limited only slightly.
To the extent that the above-mentioned components have to be cooled, they are connected by way of at least one cooling circuit to at least one heat exchanger, which is situated in the front area of the motor vehicle. In addition to the internal-combustion engine, mainly the electric motor, as well as the fuel cell, have to be cooled. The electronic power unit also normally requires separate heat removal as does the DC/DC converter and the inverter.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.